Urticaria, better known as "hives", is a common allergic reaction in which raised red or whitish areas (called weals or welts) sometimes surrounded by a red rash appear on the skin. There can be one or many hives that vary in size and shape. Hives are typically quite itchy and can last just a few minutes or several days before going away. Occasionally, however, these annoying blotches can signal more serious problems, especially when accompanied by symptoms such as difficulty in breathing.
Related to and sometimes coexisting with hives is a condition known as angioedema, which involves larger areas and deeper tissues beneath the skin. Angioedema can cause disabling swelling of internal organs, severe, uncontrollable intestinal contractions, and, if the swelling occurs in the throat blocking the air passages, it can cause suffocation.
Chronic urticaria (occuring daily for several weeks) is due to an auto-antibody in about 25% of cases. It is therefore an auto-immune disease. It is not dangerous, but is very uncomfortable and often debilitating.
Urticaria and angioedema are reactions in the skin and underlying skin tissue to histamine and other chemicals released by specialised cells called mast cells. Histamine is released in response to an invading substance your body perceives as dangerous (allergens).
It is easiest to identify drugs, foods and plants that may cause you to have hives because the response usually occurs within an hour. Hives that recur over weeks or months are more difficult to explain. If emotional stress or multiple allergies trigger your hives, finding the cause may be virtually impossible. Common allergens include:
- Insect stings or bites
- Allergy shots
- Drugs such as penicillin or aspirin
- Unwitting long-term use of a food additive, preservative or food colourant, such as tartrazine (rare)
- Infections – hives sometimes follows viral infections such as hepatitis, infectious mononucleosis (glandular fever), and German measles.
- Emotional stress
- Certain foods, particularly eggs, shellfish, nuts and fruits. Sometimes hives erupt suddenly after you’ve eaten a tiny amount of a food. Other times, hives occur only after eating large amounts (for example, strawberries).
To determine the cause of your hives, the doctor may suggest that you:
- Keep a detailed diary of everything you eat, drink, take, or are exposed to for two to four weeks
- Avoid foods, one at a time, to which you think you may be allergic
- See an allergist for skin tests (although seldom helpful)
People who are especially sensitive to heat may develop a condition called cholinergic urticaria: small, intensely itchy individual hives, each surrounded by a ring of redness. Cholinergic urticaria is brought on by exercise, emotional stress, or any activity that causes sweating.
Urticaria of pregnancy is an itchy rash that occurs during pregnancy (uncommon).
Angioedema that recurs with no sign of ordinary hives may be a disorder called hereditary angioedema. Chronic cases of hives that do not itch but are accompanied by abdominal pain or diarrhoea may be the result of hereditary angioedema.
Itching is usually the first symptom of hives, quickly followed by weals – smooth, whitish, and slightly elevated areas that usually remain small (less than 15 mm across), sometimes surrounded by a red rash. When the weals are larger (up to 20 cm across), the centre areas may be clear, so that rings are formed. Hives tend to erupt in clusters and ordinarily crops of hives come and go; one spot may remain for several hours, then disappear only to reappear elsewhere. Hives may appear on any part of the body, but are most common on the arms, legs and trunk.
With angioedema, the swelling is below the surface of the skin. It burns rather than itches and often occurs around the eyes and lips, less frequently on the hands and feet, and rarely inside the throat, on mucous membranes lining the mouth, throat and airways, or on the genitals.
When to see a doctor
If you develop symptoms of angioedema, especially of the head and neck, seek medical attention before the condition spreads to the throat or tongue and blocks the air passage to the lungs. If burning or itchy welts are already beginning to develop in your throat, or you have difficulty swallowing or breathing, seek emergency treatment immediately – you could be at risk of suffocation.
If you simultaneously develop hives and symptoms such as a dry throat, cough, fever, nausea, dizziness, abdominal cramps, shortness of breath or a sharp drop in blood pressure immediately after a bee sting, insect bite or drug injection, you may be experiencing a severe allergic reaction known as anaphylaxis. This severe shock to the immune system requires prompt medical attention. In rare cases, failure to get help quickly can be fatal.
Inform a doctor if you develop hives after a blood transfusion. You could be having an allergic reaction to donor blood.
When hives appear suddenly and disappear quickly without a recurrence, a medical examination usually isn’t needed; it rarely reveals a cause other than whatever was obvious to begin with. But when angioedema or hives recur without explanation, a medical evaluation is advisable. In order to diagnose hives or angioedema, your doctor will examine the affected area and ask about your history of sensitivity to the common allergens listed above as well as plants and pollens, animal fur, and exposure to heat, cold or sunshine. The first step in controlling hives is to identify the cause, if possible. Once you have identified the source of the problem, try to avoid exposure to it in future. Stress control may help to reduce the frequency and severity of attacks.
Hives that appear suddenly generally disappear without any treatment within days and sometimes within minutes. To relieve the itching, you could soak in a lukewarm bath, or apply calamine lotion or a cold compress to the area. Avoid heating or rubbing, which releases more histamines.
A longer-lasting case of hives should respond to an over-the-counter oral antihistamine. If the cause isn’t obvious, stop taking all non-essential drugs until the reaction subsides.
Antihistamines are the main treatment for urticaria. Your doctor will prescribe a course of prescription antihistamines such as diphenhydramine, chlorpheniramine or hydroxyzine to relieve the itching and reduce the swelling.
Prednisone, an oral corticosteroid, may reduce very severe swelling and itching, but it is usually reserved for severe cases of angioedema in which suffocation or other complications are indicated. Because corticosteroids taken for more than three to four weeks cause many adverse effects, they are prescribed only when all other treatments have failed and are given for as short a time as possible.
Ultraviolet light treatments are effective for hives caused by exposure to cold. Cold urticaria is very uncommon. About half the time, untreated chronic hives disappear within two years.
If you have symptoms of angioedema of the head and neck, you will receive an injection of antihistamine, such as diphenhydramine, to prevent the condition spreading to the throat or tongue and blocking your air passage. If it has already spread and you are at risk of suffocation, you will be given an epinephrine (adrenaline) injection along with antihistamines. Treatment is best continued in the emergency section of a hospital where your progress can be carefully monitored and medication adjusted as needed.
The first step in controlling hives is to identify the cause, if possible. Once you have identified the source of the problem, try to avoid exposure to it in future. Stress control may help to reduce the frequency and severity of attacks.
Reviewed by Prof Eugene Weinberg, Allergy Diagnositc Unit, UCT Lung Institute.